A camera module is one of the major devices used to input and output information transmitted in a digital form. Camera modules are installed in mobile phones, laptop computers, digital cameras, digital video cameras, and other devices, and some of the camera modules have imaging functions including not only a still imaging function but also a dynamic monitoring function (such as a rear monitoring function for an automobile).
Fixed-focus camera modules are installed in mobile phones etc. However, such a camera module as a whole could not be mounted using the surface mount technology (abbreviated as SMT) because there was no plastic lens that can withstand reflow soldering (in which a material is placed on a substrate coated with a solder paste by, for example, printing and then the solder is melted in a reflow furnace to secure the material to the substrate). Therefore, to address this issue, in a conventional assembling process, module components other than a lens section are surface-mounted on a substrate, and then the lenses are attached. Alternatively, after the entire camera module is assembled, it is attached to the substrate using a different method.
Low-cost plastic lenses that can withstand reflow soldering have recently been developed, allowing the entire camera module to be surface-mounted. In such circumstances, a liquid crystal polymer having high heat resistance and thin-wall moldability is being used for a “lens barrel section (a section in which lenses are installed),” a “mount holder section (a section to which the barrel is attached to secure it to a substrate),” a “frame of a CMOS (an image sensor),” “a shutter and a shutter bobbin section” (see Patent Literature 1). A recent trend is to use a liquid crystal polymer for camera module components. This significantly facilitates a reduction in size of camera modules and also significantly facilitates a reduction in size and thickness of each module component. Such a liquid crystal polymer has flame retardation without adding a halogen-based flame retardant. Therefore, to meet the demand for halogen-free plastics used for recent environmental measures, liquid crystal polymers are increasingly used for these components.
In a camera module equipped with a general fixed-focus optical system, a CMOS (an image sensor) is configured by mounting a multilayer chip on a signal processing chip. In the process of assembling the camera module, the focus of the optical component system must be adjusted manually (a lens barrel section screwed into a mount holder is rotated and moved to change the distance between the lens and the image sensor so that the focal distance is optimized) (see Patent Literature 1). However, with a conventional liquid polymer resin composition, powders (particles) of the resin composition fall off the rubbing contact portion of screws both in the lens barrel and the mount holder and the surfaces of these molded components when the lens barrel is rotated and moved in the focus adjusting step. These particles fall onto the COMS image sensor or a filter (an IR cut filter), and this is one of the main causes of image defects. Such falling of particles may also occur during the use of a product to which such components are installed. Therefore, there is a demand to provide a liquid crystal polymer resin composition that is used as the material for the lens barrel section, mount holder section, CMOS (image sensor) frame, shutter, and shutter bobbin section of a camera module and causes only a small amount of particles to fall off.
The driving methods for the camera module of a camera having an autofocus function include a voice coil motor system and a piezoelectric motor system. In the voice coil motor system, the coil is attached to the outer circumference of a lens holder for holding a lens, and a ring-shaped magnet housing (which may be referred to a case to which a magnet is attached) is disposed so as to surround the lens holder, as shown in, for example, the drawings in Patent Literature 2. The focus is adjusted by moving the lens holder in an optical axis direction using an electromagnetic induction phenomenon. A problem when a conventional liquid crystal polymer resin composition is used for the voice coil motor system is that, when, for example, a mobile phone is dropped and a shock is applied to its camera module, the lens holder inside the camera module comes into collision with the magnet housing or a base section (the surface to which the IR filter is secured). This results in dents on the surfaces of these components, causing the operation failure of the camera module.
In the structure for the piezoelectric motor system, a vibrating member such as a carbon shaft serving as a driving shaft is connected to one expanding direction end of a piezoelectric element that expands and contracts when voltage is applied, and a lens holder holding a lens is friction-fitted with the driving shaft so as to be movable in the axial direction of the driving shaft. The driving shaft is arranged in parallel to the optical axis of the lens. The lens holder is driven in the optical axis direction when the vibrating member used as the driving shaft expands and contracts according to the expanding-contracting vibration of the piezoelectric element, and the focal point can thereby be adjusted (see, for example, Patent Literature 3). A problem when a conventional liquid crystal polymer resin composition is used is that a driving failure (a reduction in driving sensitivity) occurs because the contact between the carbon shaft used as the driving shaft and the fitting surface of the lens holder becomes irregular.
One cause of the above problems may include the fact that the surface hardness of the camera module components is low.
A molded product for camera module components has been proposed in which glass fibers are added to a liquid crystal polymer to reduce the occurrence of particles (see Patent Literature 4). However, there is no description about the surface hardness of the molded product. Patent Literature 5 proposes a resin composition for a resin-made reflecting plate for, for example, a LED. In this resin composition, titanium oxide serving as a white pigment is added to a liquid crystal polyester resin to improve the reflectivity and hue. However, there is no finding about the surface hardness of a molded product and the occurrence of particles. Patent Literature 6 proposes a thin high-stiffness material obtained by mono-dispersing 1 to 5 parts by weight of silica fine particles having an average particle diameter of 0.08 to less than 0.2 μm in 100 parts by weight of liquid crystal polyester. However, the particle diameter range and amount added of the silica fine particles are different from those in the present invention, and there is no finding about the surface hardness of a molded product and particles falling off its surface.